1. Field of the Invention
The present invention relates to a wafer holder for a semiconductor manufacturing apparatus. In particular, the invention relates to a heater holder or an electrostatic chuck holder with heater which serves a function of holding a wafer while heating it.
2. Description of the Background Art
For etching of a semiconductor wafer surface or depositing of a film thereon, a method has been employed according to which gas for etching or for film deposition is supplied through the batch processing to a large number of wafers held on racks, and then the wafers are heated as required from the outer periphery (hot wall method).
However, as requirements become severer for higher integration and speed of semiconductor devices, a problem arises of non-uniform etching and unequal quality of completed films due to difference in temperature and gas flow depending on the location in the apparatus. Then, the single wafer processing (susceptor heating) has gradually been employed instead in which a plurality of etching apparatuses and film deposition apparatuses are arranged side by side and wafers are transported automatically by a loader through the apparatuses where the wafers are processed one by one. For the purpose of uniformly heating these wafers, a method is employed according to which the loader places a wafer on a holder in a chamber of the etching apparatus or the film deposition apparatus, the wafer is secured to the holder by an electrostatic chuck or statically fastened to the holder by enhancing surface precision of a wafer supporting surface of the holder, and then heat is directly applied from the holder to uniformly heat the wafer. It is thus necessary that at least a portion of the holder, which is in contact with the wafer, is formed of a material having corrosion resistance against a highly corrosive gas such as halogen gas and the like and having a high heat conductivity, and that the holder itself has an electrostatic chuck function and a mechanically fixing function as well as a heater function.
Aluminum nitride has been noticed as a candidate for the holder material because of its corrosion resistance and high heat conductivity. The high heat conductivity of the aluminum nitride allows heat generated from heater lines to spread immediately, achieving high-speed heating of the wafer as well as uniform heating of the inside of the aluminum nitride holder. Therefore, the aluminum nitride is suitable for uniformly heating a wafer.
However, regarding the holder as described above, heat generated from the heater is transmitted in not only the direction of the wafer holding surface but all directions immediately. Accordingly, the heat is also transmitted toward the backside of the holder opposite the wafer holding surface. As a result, energy is wastefully consumed leading to a great energy loss.
There is another problem that a considerable degradation occurs on the backside of the holder due to heating thereof, where there are provided line electrodes, line or the like extending from a terminal of a temperature measurement device provided for temperature control, and a seal between the holder and the chamber.
If the holder is produced by providing a wire or coil of Mo or the like between compact pieces of aluminum nitride and hot-pressing them, or by stacking a plurality of compact pieces of aluminum nitride having surfaces to which paste of refractory metal such as W and Mo is applied and simultaneously sintering them, the same aluminum nitride materials are located on and under a heater respectively so that the same amount of heat generated from the heater is transmitted not only to the material on the heater but to the material under the heater.
Then, the holder is formed into a structure having its backside reduced in size relative to the front side so as to restrict heat transmission to the backside. Nevertheless, as long as the backside is made of aluminum nitride having a high heat conductivity, the heat transmission cannot be avoided completely.
One object of the present invention is therefore to provide a wafer holder for a semiconductor manufacturing apparatus that can prevent heat from spreading toward the backside opposite a wafer holding surface of the wafer holder.
According to one aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a heater and a pair of ceramic base members with the heater interposing therebetween. The wafer holder has a wafer holding surface and a backside surface opposite each other with the heater therebetween. The wafer holder is characterized in that the ceramic on the backside relative to the heater has a lower heat conductivity than that of ceramic on the wafer holding surface side relative to heater.
According to the one aspect of the invention, in the wafer holder for a semiconductor manufacturing apparatus, the ceramic on the backside relative to the heater has a lower heat conductivity than that of the ceramic on the wafer holding surface side, so that it is possible to prevent heat from escaping toward the portion under the heater (backside) and thus efficiently heat a wafer located on the wafer holding surface. In this way, the wafer can be heated quickly, and further, degradation of seal provided under the holder can be avoided.
According to another aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a heater and a pair of ceramic base members with the heater interposing therebetween, and has a wafer holding surface and a backside surface opposite each other with the heater therebetween. The wafer holder is characterized in that a heat insulating layer is formed on the backside relative to the heater.
According to the another aspect of the invention, in the wafer holder for a semiconductor manufacturing apparatus, the heat insulating layer is formed on the backside relative to the heater, so that it is possible to prevent heat from escaping toward the portion under the heater (backside) and thus efficiently heat a wafer located on the wafer holding surface. In this way, the wafer can be heated quickly, and further, degradation of seal provided under the holder can be avoided.
According to a further aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a heater and a pair of ceramic base members with the heater interposing therebetween, and has a wafer holding surface and a backside surface opposite each other with the heater therebetween. The wafer holder is characterized in that a gap is provided between the backside surface and the heater of the wafer holder.
According to the further aspect of the invention, in the wafer holder for a semiconductor manufacturing apparatus, the gap provided under the heater serves as a heat insulating structure, so that it is possible to prevent heat from escaping toward the portion under the heater (backside) and thus efficiently heat a wafer located on the wafer holding surface. In this way, the wafer can be heated quickly, and further, degradation of seal provided under the holder can be avoided.
According to a still further aspect of the invention, a wafer holder for a semiconductor manufacturing apparatus includes a heater and a pair of ceramic base members with the heater interposing therebetween, and has a wafer holding surface and a backside surface opposite each other with the heater therebetween. The wafer holder is characterized in that ceramic on the backside relative to the heater has a lower heat conductivity than that of ceramic on the wafer holding surface side, a heat insulating layer is formed on the backside relative to the heater, and a gap is provided between the backside surface and the heater of the wafer holder.
According to the still further aspect of the invention, the wafer holder for a semiconductor manufacturing apparatus can provide a combination of heat insulating effects achieved respectively by the lower heat conductivity of the backside ceramic material than that of the ceramic material on the wafer holding surface side, the heat insulating layer formed on the backside relative to the heater, and the gap provided under the heater. As a result, the wafer can be heated more quickly and degradation of seal provided under the holder can further be prevented.
Preferably, in the wafer holder for a semiconductor manufacturing apparatus, the ceramic base member that is on the backside is formed of a material having a heat conductivity of at most 100 W/mK.
Accordingly, the ceramic material on the backside can have a heat insulating function.
Preferably, in the wafer holder for a semiconductor manufacturing apparatus, an intermediate layer is formed between the heater and the ceramic base member on the backside, and the intermediate layer is a joint layer having a heat conductivity of at most 10 W/mK.
Accordingly, the joint layer can have a heat insulating function.
Preferably, in the wafer holder for a semiconductor manufacturing apparatus, the joint layer has a thickness of at least 10 xcexcm.
The heat insulating function of the joint layer can thus be enhanced.
Preferably, in the wafer holder for a semiconductor manufacturing apparatus, the ceramic base members are formed of a material including at least one selected from the group consisting of aluminum nitride, aluminum oxide, silicon nitride and silicon carbide.
A material having corrosion resistance as well as a high heat conductivity can thus be selected properly.
Preferably, in the wafer holder for a semiconductor manufacturing apparatus, the gap has a thickness of at least 0.01 mm.
The heat insulating function of the gap can thus be enhanced.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.